U.S. patent application number 15/432580 was filed with the patent office on 2017-06-01 for method for determining an orthogonality error between two sensor signals.
This patent application is currently assigned to CONTINENTAL AUTOMOTIVE GMBH. The applicant listed for this patent is CONTINENTAL AUTOMOTIVE GMBH. Invention is credited to Jens Gleissberg, Markus Irth.
Application Number | 20170153127 15/432580 |
Document ID | / |
Family ID | 53836097 |
Filed Date | 2017-06-01 |
United States Patent
Application |
20170153127 |
Kind Code |
A1 |
Gleissberg; Jens ; et
al. |
June 1, 2017 |
METHOD FOR DETERMINING AN ORTHOGONALITY ERROR BETWEEN TWO SENSOR
SIGNALS
Abstract
The disclosure relates to a method for determining a corrected
rotation angle of a raw rotation angle recorded using an angle
sensor which, on the basis of the raw rotation angle, outputs first
and second raw rotation angle signals which have a periodic profile
and are in an orthogonal relationship with one another. A deviation
from the orthogonal relationship between the sensor signals can
occur based on the error. The method includes: determining a
correction value by means of a determination unit for determining
the correction value and making the correction value available to a
correction unit, applying the correction value to at least one of
the raw rotation angle signals by means of the correction unit for
determining at least one corrected rotation angle signal, and
calculating the corrected rotation angle using at least one of the
corrected rotation angle signals.
Inventors: |
Gleissberg; Jens;
(Schwalbach a.Ts., DE) ; Irth; Markus;
(Mainz-Kastel, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONTINENTAL AUTOMOTIVE GMBH |
Hannover |
|
DE |
|
|
Assignee: |
CONTINENTAL AUTOMOTIVE GMBH
Hannover
DE
|
Family ID: |
53836097 |
Appl. No.: |
15/432580 |
Filed: |
February 14, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2015/068711 |
Aug 13, 2015 |
|
|
|
15432580 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01D 5/24476
20130101 |
International
Class: |
G01D 5/244 20060101
G01D005/244 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 13, 2014 |
DE |
10 2014 216 224.6 |
Oct 7, 2014 |
DE |
10 2014 220 331.7 |
Claims
1. A method for determining a corrected rotational angle of a raw
rotational angle captured by means of an angle sensor, said angle
sensor outputting first and second raw rotational angle signals
depending on the raw rotational angle, said raw rotational angle
signals having a periodic profile and being orthogonal to one
another, wherein a deviation from the orthogonal relationship
between the sensor signals may occur on account of the error, said
method comprising the following steps: determining a correction
value by means of an determining unit for determining the
correction value and providing the correction value to a correction
unit; applying the correction value to at least one of the raw
rotational angle signals by means of the correction unit for
determining at least one corrected rotational angle signal; and
calculating the corrected rotational angle on the basis of at least
one of the corrected rotational angle signals.
2. The method of claim 1, wherein the rotational angle signals
corrected by means of the correction value (y) are ascertained for
both raw rotational angle signals and the corrected rotational
angle is calculated by means of both corrected rotational angle
signals.
3. The method of claim 1, wherein the corrected rotational angle
signals are normalized to form normalized rotational angle signals
having a value range between -1 and 1.
4. The method of claim 3, wherein the corrected raw rotational
angle signals, preferably the normalized raw rotational angle
signals, are retrieved continuously for determining the correction
value.
5. The method of claim 3, wherein the corrected rotational angle
signals or the normalized rotational angle signals are retrieved
depending on the corrected rotational angle for determining the
correction value.
6. The method of claim 1, wherein determining the correction value
comprises the following steps: forming a radius signal by means of
the sum of squares of the corrected or normalized raw rotational
angle signals; determining the 2*n-th harmonic of the radius
signal, where n equals a positive integer; and determining the
error on the basis of a value of the amplitude, phase shifted by
90.degree. in relation to the rotational angle, at the second
harmonic.
7. The method of claim 5, wherein the second or 2*n-th harmonic of
the radius signal is ascertained by means of a Fourier
transform.
8. The method of claim 6, wherein the imaginary component of the
second or 2*n-th harmonic of the radius signal is used for
calculating the correction value.
9. The method of claim 5, wherein the correction value is
calculated using equation: y=.SIGMA.2*arcsin(e_2*n,im) or, using
equation: y=.SIGMA.2*e_2*n,im, where e_2*n,im is the value of the
imaginary component of the second or 2*n-th harmonic.
10. The method of claim 6, wherein the value of the imaginary
component of the harmonic is only determined at planned rotational
angles.
11. The method of claim 9, wherein the values of the imaginary
component of the harmonic is calculated at the rotational angles
x_ST={0, 1, 1*2.pi./N, 2*2.pi./N, . . . , (N-1)*2.pi./N}, where N
is a positive integer.
12. The method of claim 1, wherein the correction value is set once
for each sensor.
13. An angle sensor arrangement comprising a sensor unit for
capturing the raw rotational angle signals and an evaluation unit
for carrying configured to execute a method for determining a
corrected rotational angle of a raw rotational angle captured by
means of an angle sensor, said angle sensor outputting first and
second raw rotational angle signals depending on the raw rotational
angle, said raw rotational angle signals having a periodic profile
and being orthogonal to one another, wherein a deviation from the
orthogonal relationship between the sensor signals may occur on
account of the error, said method comprising the following steps:
determining a correction value by means of an determining unit for
determining the correction value and providing the correction value
to a correction unit; applying the correction value to at least one
of the raw rotational angle signals by means of the correction unit
for determining at least one corrected rotational angle signal; and
calculating the corrected rotational angle on the basis of at least
one of the corrected rotational angle signals.
14. A drive device comprising an electric motor, in particular for
a driver assistance apparatus, a control device for controlling the
electric motor, and comprising an angle sensor arrangement
including a sensor unit for capturing the raw rotational angle
signals and an evaluation unit for carrying configures to execute a
method for determining a corrected rotational angle of a raw
rotational angle captured by means of an angle sensor, said angle
sensor outputting first and second raw rotational angle signals
depending on the raw rotational angle, said raw rotational angle
signals having a periodic profile and being orthogonal to one
another, wherein a deviation from the orthogonal relationship
between the sensor signals may occur on account of the error, said
method comprising the following steps: determining a correction
value by means of an determining unit for determining the
correction value and providing the correction value to a correction
unit; applying the correction value to at least one of the raw
rotational angle signals by means of the correction unit for
determining at least one corrected rotational angle signal; and
calculating the corrected rotational angle on the basis of at least
one of the corrected rotational angle signals.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of PCT Application
PCT/EP2015/068711, filed Aug. 13, 2015, which claims priority to
German Application DE 10 2014 216 224.6, filed Aug. 14, 2014 and
German Application DE 10 2014 220 331.7, filed Oct. 7, 2014. The
disclosures of the above applications are incorporated herein by
reference.
TECHNICAL FIELD
[0002] The disclosure relates to a method for determining a
corrected rotational angle of a raw rotational angle captured by
means of an angle sensor, an angle sensor arrangement and a drive
device for carrying out such a method.
BACKGROUND
[0003] The prior art has disclosed the document DE 10 2010 003 201
A1, which discloses a method for determining a rotational angle
using an angle measuring unit. This document discloses how the
rotational angle may be corrected by means of a correction value
such that the influence of a phase displacement F on the value of
the rotational angle is reduced. This relates to an error resulting
from orthogonality between a sine-shaped sensor signal and a
cosine-shaped sensor signal of the sensor element not being quite
exact.
[0004] Further, the application DE 10 2014 216 224.6, which
establishes the priority, discloses a method which highlights a
different option to the one in the aforementioned document for
determining the orthogonality error or a correction value for
correcting the orthogonality error between the two angle
signals.
SUMMARY
[0005] The disclosure highlights an option which allows a corrected
rotational angle calculation or determination to be carried out
precisely and in a simple manner.
[0006] One aspect of the disclosure provides a method, by means of
which determining the correction value and introducing the
correction value into the rotational angle calculation may be
integrated into existing processes as easily as possible. Based on
the method, in particular the determining unit, it is possible to
implement the error correction in an already established operation
in a particularly flexible manner. Moreover, it is possible to
adapt the options for calculating or determining the correction
value according to requirements, for example depending on
requirements relating to the accuracy of the calculation of the
correction value. In contrast to the prior art, a determining unit
for determining the correction value is used in addition to a
correction unit. In this way, it is possible to flexibly set the
manner in which the correction value is established in the
determining unit.
[0007] The method is developed such that rotational angle signals
corrected by means of the correction value are ascertained for both
raw rotational angle signals and the corrected rotational angle are
calculated by means of both corrected rotational angle signals.
This ensures that both raw rotational angle signals are corrected
in such a way that they substantially assume their setpoint
values.
[0008] The method may be developed such that the corrected
rotational angle signals are normalized to form normalized
rotational angle signals, for example, to a value range between -1
and 1. By means of the normalization, the corrected rotational
angle signals are prepared in such a way that determining the
corrected rotational angle may be carried out independently of the
scaling of the raw rotational angle signals. The method according
to the disclosure may therefore be applied to a multiplicity of
sensor types.
[0009] Thus, according to the disclosure, a method for determining
a corrected rotational angle (x_tl) of a raw rotational angle (x),
or angle sensor signal, captured by means of an angle sensor is
proposed. The angle sensor outputs first and second raw rotational
angle signals (s_r, c_r), or sensor signals, depending on the raw
rotational angle (x). The said raw rotational angle signals or
sensor signals have a periodic profile and are orthogonal to one
another. A deviation from the orthogonal relationship between the
sensor signals may occur on account of the error (y). The method
includes the following steps: determining a correction value (y) by
means of a determining unit for determining the correction value
(y) and providing the correction value (y) to a correction unit,
applying the correction value to at least one of the raw rotational
angle signals (s_r, c_r) by means of the correction unit for
determining at least one corrected rotational angle signal (s_oc,
c_oc), and calculating the corrected rotational angle (x_tl) on the
basis of at least one of the corrected rotational angle signals
(s_oc, c_oc).
[0010] Implementations of the disclosure may include one or more of
the following optional features. The method according to the
disclosure is advantageously developed such that the corrected raw
rotational angle signals, preferably the normalized raw rotational
angle signals, are retrieved continuously for determining the
correction value. The so-called online determination of the
correction value allows an even more precise determination of the
correction value. In this way, the external influences on the raw
rotational angle signals, and also other influences which lead to a
change in the orthogonality error, may be taken into account
continuously. This also allows an oscillation behavior of the
orthogonality error to be taken into account continuously in the
correction value as well. Particularly in the case of applications
in the automotive branch, for example in the case of driver
assistance, this example may be particularly advantageous for
determining an exact driver assistance torque.
[0011] In some implementations, determining the correction value
includes the following steps: forming a radius signal by means of
the sum of squares of the corrected or normalized raw rotational
angle signals, determining the 2*n-th harmonic of the radius
signal, where n equals a positive integer, and determining the
error on the basis of a value of the amplitude, phase shifted by
90.degree. in relation to the rotational angle, at the second
harmonic.
[0012] This way of determining the error correction may be
implemented in a particularly simple manner and was found to be a
particularly stable and accurate method for determining the error
correction. It may be carried out both online and offline. The
advantage of this implementation lies in the fact that the error is
established based on the radius signal, which may be determined
merely on the basis of the two raw rotational angle signals. Since
these signals are needed in any case for determining the rotational
angle, there is no need to change the existing rotational angle
sensors. There is no need for a reference sensor signal, to which
the sensor signals could be compared individually, in order to
ascertain the error in the individual sensor signals. The method
may therefore be integrated particularly easily into existing
systems since the electronic means required for evaluating the
sensor signals are present in any case.
[0013] The mathematical derivation emerges as follows below. The
amplitude of the radius signal may be mapped by means of the
equation:
e_orth(x)=sin.sup.2(x)+cos.sup.2(x+y), (1)
where x represents the value of the rotational angle and y
represents the value of the error. To the extent that the error
y=0, the aforementioned condition of the addition theorem is
satisfied.
[0014] Inter alia, the amplitude of the radius signal has a maximum
at an angle of 45.degree., and so the radius signal assumes the
following value at x=45.degree.:
e_orth (45.degree.)=1-sin(y). (2)
[0015] For the purposes of determining e_orth(45.degree. from the
measured signals, it is necessary to mask other errors in the
radius signal e_orth(x) or e. This may be carried out by a harmonic
analysis by means of the Fourier transform. Here, the magnitude of
the imaginary part of the 2.sup.nd harmonic corresponds to the
value e_orth (45.degree. as a result of the Fourier transform.
Here, the complete suppression of other errors in the signal
e_orth(x) is advantageous by only considering the second harmonic,
such as e.g., offset, gain or axial-offset errors, as these do not
act on the second harmonic. Since the amplitudes are calculated as
a result of the Fourier transform, but y describes the peak-to-peak
value (from the minimum value to the maximum value), the magnitude
of the imaginary part of the 2.sup.nd harmonic needs to be
doubled:
y=arcsin [2*(e_orth,2*n.,im)] (3)
[0016] The method according to the disclosure is advantageously
developed such that the second or 2*n-th harmonic of the radius
signal being ascertained by means of a Fourier transform,
preferably a discrete Fourier transform. The discrete Fourier
transform facilitates carrying out the aforementioned method with
as little computational outlay as possible.
[0017] The method according to the disclosure is advantageously
developed such that the imaginary component of the second or 2*n-th
harmonic of the radius signal being used for calculating the
correction value. This example is based on the idea of the error
directly acting on the amplitude of the second harmonic, or an
integer multiple of the second harmonic, of the radius signal and
hence of an analysis of the amplitude of the second harmonic
providing direct conclusions about the magnitude of the error. For
example, this example is based on the discovery that the error in
the second harmonic of the radius signal occurs with a phase shift
of 90.degree. in relation to the rotational angle, and so the
imaginary component of the harmonic provides conclusions about the
error.
[0018] The method according to the disclosure is advantageously
developed such that the correction value being calculated on the
basis of the equation:
y=.SIGMA.[arcsin(2*e_2*n,im)] (4)
or, preferably, on the basis of the equation
y=.SIGMA.[2*e_2*n,im] (5)
where e_2*n,im is the value of the imaginary component of the
second or 2*n-th harmonic. In some examples, the latter
simplification highlights an option, by means of which the
computational outlay for determining the correction value may be
reduced further. Here, this is based on the assumption that the
correction value generally lies within a small value range around
zero, and hence this assumption leads to a simplified calculation
for a multiplicity of applications.
[0019] The method according to the disclosure is advantageously
developed such that the value of the imaginary component of the
harmonic being only ascertained at planned rotational angles
(x_ST). This ensures that the imaginary component of the 2.sup.nd
or 2*n-th harmonic for an angle is not calculated a number of times
within one rotation.
[0020] The method according to the disclosure is advantageously
developed such that the values of the imaginary component of the
harmonic being calculated at the rotational angles:
x_ST={0, 1, 1*2.pi./N, 2*2.pi./N, . . . , (N-1)*2.pi./N}, (6)
where N is a positive integer. This fixes the calculation of the
imaginary component to fixed angles or angle positions. This is
advantageous in that the calculation of the imaginary component may
be established independently of the speed with which the rotational
angle changes.
[0021] The method according to the disclosure is advantageously
developed such that the correction value being set once for each
sensor. The so-called offline calculation or ascertainment of the
correction value requires little outlay based on the single
calculation and may also be carried out by means of external
computer units, as result of which production costs of sensor
arrangements may be kept low.
[0022] Furthermore, another aspect of the disclosure provides an
angle sensor arrangement that includes a sensor unit for capturing
the raw rotational angle signals and an evaluation unit for
carrying out a method according to one of the previously describes
aspect of the disclosure and examples thereof.
[0023] Further, another aspect of the disclosure provides means of
a drive device that includes an electric motor, in particular for a
driver assistance apparatus, a control device for controlling the
electric motor, and including an angle sensor arrangement according
to the previously mentioned aspect of the disclosure.
[0024] The details of one or more implementations of the disclosure
are set forth in the accompanying drawings and the description
below. Other aspects, features, and advantages will be apparent
from the description and drawings, and from the claims.
DESCRIPTION OF DRAWINGS
[0025] The disclosure below is described in more detail according
to examples and a plurality of figures. In the figures:
[0026] FIG. 1 illustrates a basic structure of an angle sensor for
an angle sensor arrangement,
[0027] FIG. 2 illustrates an exemplary illustration of an
orthogonality error in the angle sensor,
[0028] FIG. 3 illustrates a block diagram of an angle sensor
arrangement for carrying out the method according to the
disclosure,
[0029] FIG. 4 illustrates a detailed illustration of an determining
unit from the block diagram in FIG. 3,
[0030] FIG. 5 illustrates a block diagram for carrying out a
comparison test between an absolute setpoint angle value and the
corrected rotational angle, and
[0031] FIGS. 6-8 illustrate a comparison of the results with and
without rotational angle correction.
[0032] Some of the reference signs in the figures respectively have
an index written as a subscript which, alternatively, is described
by means of the sign " " in the subsequent description.
[0033] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0034] FIG. 1 shows the structure of an angle sensor 101 that is
used in an angle sensor arrangement 100 shown in FIG. 3. Firstly,
the angle sensor 101 includes an angle transducer 102. The angle
transducer 102 predetermines a rotational angle signal x, which is
captured by two sensor elements 103s, 103c. Each sensor element
103s, 103c generates a raw rotational angle signal s_r and c_r from
the rotational angle signal x of the angle transducer 102. The raw
rotational angle signal is used to calculate or determine the
corrected rotational angle x_tl.
[0035] The raw rotational angle signals s_r, c_r are periodic
signals in each case, for example a sine signal and a cosine
signal, which have a 90.degree. phase shift in relation to one
another. Due to the orthogonal relationship between the sensor
signals, the sensor signals may observe the condition according to
the addition theorem sin.sup.2(x)+cos.sup.2(x)=1, where x is the
value of the rotational angle. There may be a deviation from the
orthogonal relationship between the two raw rotational angle
signals s_r and c_r for a number of different reasons which, for
example, may occur once during the production of the angle sensor
102 or due to external influences during operation, which are
permanently present. An error case, in which the actual raw
rotational angle signal s_r has an orthogonality error and
therefore incorrectly assumes the profile of the curve s_r_err, is
highlighted in an exemplary manner in FIG. 2. As a result, the
phase shift between the two raw rotational angle signals is not
90.degree. but 90.degree.+y. The method facilitates determining
this error as a correction value y.
[0036] FIG. 3 shows an angle sensor arrangement 100, which may be
used to carry out the method according to the disclosure. Firstly,
the angle sensor arrangement includes the angle sensor 101. The
latter is connected to a correction unit 110. The correction unit
110 in turn is connected to a normalization unit 130. The
normalization unit 130 is connected to an angle calculating unit
140. Furthermore, the angle sensor arrangement 100 includes a
determining unit 150 for determining the correction value y. The
determining unit 150 is connected to the correction unit 120 and
provides the correction value y to the latter. In some examples,
connected means a connection for transferring signals or data.
Preferably, this is a data connection. In the figures, the
connections are depicted by means of an arrow in each case. It is
not mandatory for the angle sensor arrangement to include a
normalization unit 140. However, this is advantageous.
[0037] The method is carried out in such a way that, firstly, the
determining unit 150 determines a correction value y and provides
the value to the correction unit 120. The correction value y is
applied to at least one of the raw rotational angle signals s_r,
c_r by means of the correction unit 120 for determining at least
one corrected rotational angle signal s_oc, c_oc, from which the
corrected rotational angle x_tl is calculated based on at least one
of the corrected rotational angle signals s_oc, c_oc. In this
example, it is the case that rotational angle signals s_oc, c_oc
corrected by means of the correction value (y) are established for
both raw rotational angle signals s_r, c_r and the corrected
rotational angle x_tl is calculated by means of both corrected
rotational angle signals s_oc, c_oc. Furthermore, this example may
also include the step of normalizing the corrected rotational angle
signals s_oc, c_oc to form normalized rotational angle signals s_n,
c_n. For example, the normalization is carried out in such a way
that the normalized rotational angle signals s_c, c_n then lie
within a value range between -1 and 1.
[0038] Moreover, the example has the property that the corrected
and normalized raw rotational angle signals s_n, c_n are
continuously retrieved for determining the correction value. To
this end--as may be seen in FIG. 3 --the normalized rotational
angle signals s_n, c_n are forwarded to a computer unit 151, in
which a radius signal e is calculated by means of the expression
s_n.sup.2+c_n.sup.2. Then, the correction value y is calculated or
determined in the determining unit 150 based on the radius signal.
FIG. 4 shows the structure of the determining unit 150 in more
detail.
[0039] The determining unit 150 firstly includes a DFT block 152
and secondly an integration block 153.
[0040] Within the DFT block 152, the 2.sup.nd harmonic is
calculated from the radius signal e by means of a discrete Fourier
transform. Since only the imaginary component is decisive for
determining the orthogonality error or the correction value y, it
is possible to further simplify the calculation. That is to say,
instead of carrying out the calculation by way of the equation:
e ^ 2 = j = 0 N - 1 - 4 .pi. j N * e j , ( 7 ) ##EQU00001##
the calculation may be specified further by the equation:
e ^ 2 , im = 1 N j = 0 N - 1 sin 4 .pi. j N * e j . ( 8 )
##EQU00002##
[0041] This is only carried out for specific angle positions or
angles, however. To this end, the current corrected rotational
angle x_tl is retrieved and a check 154 is carried out as to
whether the current corrected rotational angle x_tl corresponds to
a predetermined rotational angle x_ST stored in a memory. In a
first run through, the corrected rotational angle x_tl may also be
present in an uncorrected form. Preferably, the values of the
predetermined rotational angle lie at nodes x_ST, which may be set
as follows:
x_ST={0, 1, 1*2.pi./N, 2*2.pi./N, . . . , (N-1)*2.pi./N} (9)
[0042] Should this be the case, the calculation of the summand
_2,im is carried out, elucidated by the arrow 155. Calculation of
the sine signal may also be replaced by the use of a table with
sine values that fit to the position x_ST.
[0043] An individual correction value y_s shown in the below
equation:
y_s=arcsin(2* _2,im) (10)
may then be calculated from the imaginary component of the second
harmonic _2 using the equation. Due to the assumption that the
values of the imaginary component of the second harmonic lie
closely around zero, it is also possible to carry out a
simplification, namely shown in the below equation:
y_s=2* _2,im. (11)
[0044] In order to compensate the orthogonality error, the value y
must be formed from the sum;
y=y+y_s (12)
since an orthogonality error of y_s =0 would emerge when feeding
back the determined compensation value y. The initial value of y is
0. In order to avoid sudden discontinuities in the angle signal
x_tl, the signal y may have a change restriction, which may, for
example, easily be realized by restricting the value of y_s. The
effectiveness of the method according to the disclosure will be
illustrated below in FIGS. 5 to 8.
[0045] FIG. 5 shows a structure that was used to carry out a
simulation of the method according to the disclosure. The structure
substantially corresponds to the structure of the angle sensor
arrangement 100. In order to compare the effectiveness of the angle
sensor arrangement 100 or of the method according to the
disclosure, the value of a reference sensor x_ref was used to be
able to make a comparison between the value of the reference sensor
x_ref and of the corrected rotational angle x_tl.
[0046] The raw rotational angles x were undertaken on real
resolvers with a subsequent simulation of the angle error, i.e.,
the angle error was artificially added. The signals x_ref, x_tl,
s_r and c_r were recorded. Different orthogonality errors were
used, as described below.
[0047] During the simulation, the signals s_r and c_r were
introduced into the model as stimuli. Hence, two systems for
calculating angles are realized, the systems receiving exactly the
same input data. Firstly, there is the model simulation with
automatic orthogonality compensation by means of the correction
value y. Moreover, a controller without orthogonality compensation
was also used for comparison purposes.
[0048] The angle x_tl calculated by the model may be compared to
the reference angle x_ref and forms the angle difference
x_diff,comp. Additionally, the angle error is calculated without
orthogonality compensation from the measured values of the control
device as x_diff for comparison purposes.
[0049] Both systems are provided with a time of approximately 3.2
seconds for settling before the simulation carries out the
automatic orthogonality correction. As a result, the effect can be
illustrated well visually.
[0050] FIGS. 6, 7, and 8 show the results for resolvers with the
following fed orthogonality errors: FIG. 6: 0.154.degree. el, FIG.
7: 0.655.degree. el, and FIG. 8: -0.3.degree. el.
[0051] In the upper diagram, the angle error without compensation
x_diff is depicted in each case as a red/dashed line. The
compensated value x_diff_comp is as a blue/full line. The first
value for the orthogonality error was determined at the time t=3.75
s and fed to the orthogonality compensation. The effect can clearly
be seen; the angle error no longer has a dominant 2.sup.nd
order.
[0052] In the lower diagram, the signal y as the ascertained
orthogonality error is depicted as a green/full line and the signal
y_s as the ascertained residual orthogonality error is depicted as
a blue/dashed line.
[0053] The clear reduction in the orthogonality error may be
identified in FIGS. 6 to 8. In the application shown here, the
residual angle error no longer has a critical magnitude.
[0054] The compensation value y was applied directly without
smoothing, as a result of which angle discontinuities occurred,
particularly in FIG. 7, when changing y. In return, it is easily
possible to identify how y_s assumes the value of y once, in order
subsequently to remain at the level of the identification accuracy.
If y is smoothed, the signals y and y_s exhibit transient
behavior.
[0055] It should be noted that the compensation value is the
peak-to-peak value of the harmonic angle error. It therefore has
the 2-fold value of y_s=arcsin(e_2,i,m). Furthermore, it may easily
be identified that the correction of the orthogonality error
removes the angle displacement in the order of the orthogonality
error.
[0056] In some implementations, which may be combined with the
aforementioned example are listed below.
[0057] In some examples, a method for determining an error (y)
between two sensor signals (s1, s2) in an angle sensor, which
depending on an angle transducer, outputs the sensor signals (s1,
s2). The sensor signals have a periodic profile and are orthogonal
to one another from a mathematical point of view. A deviation from
the orthogonal relationship between the sensor signals may occur
due to the error (y). The method includes the following steps:
forming a radius signal (e_orth) by means of the sum of squares of
the sensor signals; determining the 2*n-th harmonic of the radius
signal (e_orth), where n equals a positive integer; and determining
the error of a value of the amplitude, phase shifted by 90.degree.
in relation to the rotational angle value, at the second harmonic.
In some examples, the method further includes determining a
frequency component or frequency components of the radius signal by
means of a Fourier transform and determining the error on the basis
of the imaginary component of the frequency component or of the
frequency components of the second harmonic. The Fourier transform
may be carried out by means of a Fast Fourier Transform and/or
discrete Fourier transform. In some examples, the error y may be
calculated by means of equation:
y=arcsin|e_orth,2*n.,im| (13)
is established, where e_orth,2.,im maps the imaginary component of
the amplitude of the 2*n-th harmonic of the radius signal.
[0058] In some implementations, the real component of the 2*n-th
harmonic is used as a scale for a scaling error. The method may be
used during running operation.
[0059] In some examples, the method is carried out prior to
starting up an angle sensor, in particular by means of an external
computer unit.
[0060] In some implementations, a method for determining an error
(y) between two sensor signals (s1, s2) in an angle sensor which,
depending on an angle transducer, outputs the sensor signals (s1,
s2). The sensor signals have a periodic profile and are orthogonal
to one another from a mathematical point of view. A deviation from
the orthogonal relationship between the sensor signals may occur
due to the error (y). The method includes the following steps:
determining a rotational angle (x) from the sensor signals (s1,
s2); determining a conversion value by carrying out a Fourier
transform for the ascertained rotational angle; and determining the
error based on the conversion value.
[0061] In some implementations, an angle sensor for capturing a
rotational angle, includes a sensor element which outputs the
sensor signals dependent on an angle transducer. The sensor signals
have a periodic profile and are orthogonal to one another from a
mathematical point of view, and a computer unit for carrying out
the method as claimed in one of the preceding claims.
[0062] A number of implementations have been described.
Nevertheless, it will be understood that various modifications may
be made without departing from the spirit and scope of the
disclosure. Accordingly, other implementations are within the scope
of the following claims.
* * * * *